Thermal switch for fluorescent lamps



March 16, 1943. R. F. HAYs, JR., ETAL 2,313,745

THERMAL SWITCH FOR FLUORESCENT LAMPS Filed June 4, 1941 1 Z ATTGRNEY Patented Mar. 16, 1943 2,313,745 THERMAL swrrcn Foa FLUomrscENr LAMrs Robert F. Hays, Jr., Bloomfield, N. J., and Charles H. Hodgkins, Fair-Held, Conn., assignors lto Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of A Pennsylvania.

Application June 4, 1941, Serial No. 396,576

(Cl. 20o-122) 7 Claims.

The present invention relates to thermal re- 1 age higher than normal line voltage, as supplied from the customary domestic source of supply, is required to initiate a discharge, the relay iirst operates to close a heating circuit for the electrodes after which the heating circuit is interrupted and a high voltage surge momentarily impressed across the preheated electron emitting electrodes. Once the discharge has started in the lamp the relay remains dormant but should the lamp fail to start on the rst operation of the relay the latter continues in its cycle of operation until the lamp actually starts.

The diiilculty heretofore existent in relays for starting iluorescent lamps has been due to their rapidity of operation which in many instances does not allow sufiicient time to heat the electrodes of the lamp to full electron emitting .temperature. Thisresults in the impression of the high voltage surge across the lamp electrodes,

prior to their reaching maximum electron emitting temperature which causes sputtering of the electron emitting coating provided on the surface of the electrodes thus greatly reducing the useful life of the lamp. y

It is the primary object of the present invention to provide a. thermal relay for the starting of fluorescent lamps in which a suillcient time delay occurs to insure adequate heating of the lamp electrodes.

Another object of the present invention is the provision of a thermal relay particularly adaptable to the starting of uorescent lamps wherein positive engagement of the contact terminals is assured and chattering thereof eliminated.

Another object of the present invention is the provision of a thermal relay particularly adaptable to the starting of fluorescent lamps wherein Figure 1 is a front elevational view partly in cross-section of the thermal relay unit of the present invention,

Figure 2 is a side elevational view partly in cross-section of the thermal relay unit shown in Figure 1 with the elements in their normal position,

Figure 3 is a fragmentary elevational view partly in cross-section and similar to Figure 2 except that the thermal expansive element is shown in its heated position,

Figure 4 is a sectional view taken on the line IV-IV of Figure 1,

Figure 5 is a fragmentary view showing a modicaton that the contact parts of the thermal expansive element may;Av take,

Figure 6 is a view similar to Figure 5 but showing a `still further modication which the contact terminals supporting portion may take, and

Figure 7 is a schematic diagram showing a circuit for the starting of a fluorescent lamp and employing a thermal relay of the present invention.

Referring now to the drawing in detail the thermalrelay as shown in Figure l comprises a` base member 5 of suitable insulating material such as Bakelite, ber or the like, secured in an upright position to a closure member 6 also of insulating material, the latter of which forms an end for an aluminum cylinder or can 1, 4being secured thereto by means of lugs or the like 8.

A U-shaped bimetallic element 9 is secured at the end of one leg to the base member 5, such as by a rivet or the like Il), while the end of its other leg is provided with a suitable metallic contact terminal I2, such as silver, platinum, or the like.

the relay operates with positiveness and is uninfluenced by ambient temperature.

A further object of the present invention is the provision of a thermal relay particularly adaptable to the starting of fluorescent lamps wherein the thermal element is prevented from twisting in an undesired direction.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

A similar contact terminal I3 is positioned to be normally engaged by the contact terminal I2, with the former being connected through a metallic connector I4 to a socket terminal I5 carried by the closure member 6.

The xed leg of the bimetallic element 9 is provided with a corrugation I6 of substantially semicylindrical configuration and a heater element in the form of a resistance heater Il is secured, by suitable screws or rivets I8 and I 9, to the base member 5 beneath the corrugation I6. The cross-piece or base portion 20 of the U-shaped bimetallic element 9 is provided with a stiil'enlng rib 22, which may take the form ci a small corrugation, to prevent lateral twisting of the bimetallic element 9 when heated, as hereinafter more fully described. A rectangular opening 23 base portion 20 to yield in the direction of the base without coming in contact therewith and an opening 2B is likewise provided in the base member 5 adjacent the contact I3 to permit it to yield in the direction of the base.

As can be seen more readily from Figures 1 and 4 one end of the heater element I1 is connected to the bimetallic element 9 by means of a metallic strip 25 on the rear side of the base member 5 and by the rivet I0 which passes through the bimetallic element 9 and one end of the metallic strip 25. The other end of the heater element I1 is connected by a conductor 26 (Fig.' 4) to one electrode ot a glow relay tube 21 of the type such as shown and claimed in Patent 2,228,210, issued January 7, 1941 to R. F. Hays, Jr., and assigned to the same assignee as thepresent invention. The remaining electrode of the glow relay tube 21 is connected by a conductor 28 to an additional socket terminal 29 carried by the closure member 6.

For the purpose of preventing interference with radio reception during operation of the fluorescent lamp a small condenser 30 is connected in electrical parallel with the series connected glow relay tube 21 and thermal relay 9, as can be more readily appreciated by reference to Figure 1.

asians the lamentary electrodes 34 and 35 is sumcientto maintain the bimetallic electrode of the glow relay tube in a heated condition so it will continue in engagement with the other electrode of the glow relay tube. On the other hand, the glow relay tube need only be so designed that a high transient voltage will not be produced upon opening of its contacts. Since no high voltage surge,

is thus produced. premature opening of the electrodes of the glow relay causes no deleterious effect as they will again immediately close as long as full line voltage is impressed across the eleca trodes, which condition exists so long as the con- In addition, a small resistance 32 which may be wound about the condenser 33, such as shown in Figures 2 and 3, is also connected in electrical series with the condenser 33 and series connected glow relay tube 21 and thermal relay 3. All of these elements as shown are housed within the aluminum cylinder or can 1 so that an integral unit is formed which. is insertable in an appropriate socket.

By reference now more particularly to Figure 'I a circuit arrangement is shown for the starting of a nuorescent lamp 33 and in which the starting device in accordance with the present invention is employed. The lamp 33 is provided with oppositely disposed fllamentary electrodes 34 and 3l which are connected in a series heating circuit by the starting device upon closure of a suitable switch 33. Upon closure of such switch electrical energy will be supplied from the source of customary domestic potential LI-L2 with current flowing through the lamentary electrode 34 and a conductor 31, socket terminal 23, and conductor 23 to one of the electrodes of the glow relay tube 21. Full line voltage is thus impressed across the electrodes of the glow relay tube 21 since the circuit is completed through the conductor 23, heater element I1, bimetallic element 3, its normally closed contact terminals I2 and I3, metallic strip I4, socket terminal I5 and a conductor 33, filamentary electrode 33 and an inductance element 33, and switchV 33 (now closed) back to the opposite side of the source of supply L2. As pointed -out in the above mentioned patent, the application of full line voltage across the electrodes of the glow relay tube will cause a glow discharge between its electrodes. 'I'his glow discharge heats the electrodes of the glow relay tube and since one of the electrodes is a bimetallic element it is distorted into contact with the remaining electrode, thus causing engagement thereof with extinguishment of the discharge in the glow relay tube. Positive engagement of such electrodes accordingly closes a serie's heating circuit for the filamentary electrodes 34 and 35 of the lamp 33,

thus heating such electrodes to an electron emit-l ting temperature.

The bimetallic electrode of the 21 may be so designed that the 12R that the flow of current in the heating circuit glow relay tube effect is such for tacts I2 and I3 of the thermal relay 3 remain closed and the discharge is not initiated in the lamp 33. Closure of the'heating circuit not only heats the iilamentary electrodes 34 and 33, but since the heater element I1 is likewise in series in the circuit it is likewise simultaneously heated. Consequently by the time the iilamentary electrodes 34 and 33 of the lamp 33 have reached optimum electron emitting temperature, the heater element I1 will likewise be heated to a temperature suilicient to cause operation of the thermal relay or bimetallic element 3 causing operation thereof, with attendant separation of its contacts I2 and I3 as hereinafter described more in detail. This interrupts the heating circuit ior the fllamentary electrodes 34 and 33 and at thesame time causes a high transient voltage surge from the inductance 33 which initiates a discharge between the heated electrodes 34 and 33 o! the lamp 33.

During operation of the lamp 33 the thermal relaylconsumesnoenergyfromthesourceof supply, despite the fact that its contacts I2 and I3 again assume their normally closed podtion upon cooling of the bimetallic element 3 and heater element I1, and that the electrodes of the glow relay tube 21 likewise assume their normally open position upon cooling of the bimetallic electrode.'

This is because the voltage impressed across the electrodes of the glow relay tube during operation of the lamp 33 is insufiicient to again initiate a discharge in the glow relay tube 21. If for any reasonadischargeisnotinitiatedinthelamp 33 upon opening of contacts I2 and I3 of the thermal relay 3, the above described cycle will be repeated until such a discharge is initiated.

The primary function d thermal relay 3 is to inject a delay period beton its contacts I2, I3 will open. such delay acti affording the necessary time for the filamentary electrodes 34, 3l of the lamp to heat. The construction shown promotes such delay in several ways. The semicyllndricalportion Ilinthexedlegispro vided with a stliiening bead or corrugation I3' inaperipheralrelationshiptothesaidportion I3 and longitudinal direction with respect to the leg. This bead preventsthe portion I3 from bending and necessitates heat to travel by conduction therefrom to the flat portion ot the' leg beforetheiegwillbendduetotheheat. 'me semi-cylindrical portion may move bodily to and frowithrespecttotheheaterwhentheatportion of the leg bends, but does` not itself bend. Thus time lag of heat n by conduction in the leg introduces one delay action. -Additional delay action is obtained by the requirement that the contact-separating moment must be by conduction of heat toward the fixed end of the leg, and since that end is in effect the short end of a lever, more force to overcome the inherent resilient tension acting in a contactclocing direction is required.

amavis However, third, and perhaps most important means for injecting delay action in opening of said contacts I2, I3, is obtained by situating the heater within a ceramic or other tunnel or enclosure I1' which is shown best in Fig. 4. Said enclosure I1' may conveniently comprise a ceramic heat and electrical insulative tube situated lengthwise between rivets I8, I9 transverse thereto and transverse tothe bimetal leg beneath the semi-cylindrical corrugation thereof parallel to said corrugation. The heater I1 passes longitudinally through this tube or enclosure I1', and by virtue of the heat capacity of the enclosure delayed faction of heatfrom theheater to the bimetal element occurs. By these several means, therefore, ample delay of opening of contacts I2, I3 is obtained to allow the lamp filaments to become heated and the gas in the lamp' ionized for -assuring striking of the arc immediately with rst opening of said contacts.

Moreover, due to the time delay action of thev thermal relay 9 no damage is done to the lamp 33 because the thermal relay does not operate to open its contacts I2 and I3 until the fllamentary electrodes 34 and 35 havel been heated for a sufficient time to bring them up to optimum thermionic emission.

It should also be noted that the thermal relay 9 operates merely to interrupt the series heating circuit while the glow relay tube 21 operates tov optimum electron emitting temperature, as above mentioned. l

By reference now more particularly to Figures 2 and 3 it will be noted, as before mentioned, that in the normal position of the thermal relay 9 the contacts I2 and I3 are closed. Also due to the construction of the bimetallic element 3, a slight tension is applied to the;5 movable leg carrying the contact I2 soA that a positive engagement is established with the stationary contact I3. Upon heating the bimetallic element 3 by the heater element Il the fixed leg of the U- shaped bimetallic element will be distorted in the direction of the base member 5.

rThis overcomes the tension o f the movable leg in the opposite direction with the result that the contact i2 carried by the movable leg separates from the fixed contact I3. The application of heat to the lixed leg of the U-shaped birnetallic element 9 is particularly advantageous because it contributes to the required time delay before opening of the contacts i2 and I3 occurs. Moreover, in the event the contacts i2 and I3 close under load with attendant generation of heat at the contacts, the movable leg is desirably heated by the contacts so as to increase the contact pressure, thus contributing to the desired time delay and at the-same time eliminating chattering of the contacts.

Attire same time premature opening of these contacts by twisting or lateral movement of the biinetallic element is prevented by the provision ci the reinforcing rib 22. In Figures 5 and 6 two modifications are shown which operate'to accomplish the same result. The structure shown in Fig. 5 comprises a short section 40 of bimetal wherein the high expansion metall is reversed from that of the major portion 45 of the movable leg. Consequently upon heating of the contacts when closing under load the short Section 4l? is forced in the direction of the stationary contact I3 to increase the contact pressure again preventing chattering.

The modification shown in Figure 6 operates in the identical manner but differs from the previously described structures in that the end of the bimetal strip 45 is bent upon itself to provide movement of the free end in the opposite direction to the main parallel portion when subjected to heat.

Although the thermal relay 9 has thus vfar been described as forming an integral part of a complete starting unit'in combination with a glow relay tube, in instances it can itself be utilized and the glow relay tube entirely dispensed with so that `only the thermal relay and condenser remain in the casing.

It thus becomes obvious to those skilled in thev art that a thermal relay is herein provided particularly adaptable for the starting of fluorescent lamps wherein a desired time delay is provided so that its contacts remain closed and under tension for a pre-determined period of time after which separation of the contacts occurs without chattering. Moreover, the relay is so constructed that upon heating of the contacts due to arcing therebetween or other causes when closing under load, the contact tension is increased due to heat transfer from contact I2 to movable end 9 of bimetal 20.

Although several embodiments of the present invention have been shown and described it is to be understood that still further modifications thereof may be made without departing from the spirit and scope of the appended claims.

We claim:

l. A starting relay for completing a circuit to a'discharge lamp of the fluorescent type comprising a casing, a glow switch disposed in said casing and having normally separated contacts adapted to close the circuit to said lamp upon the occurrence of a glow discharge in said glow switch, a` thermal switch provided with a heatresponsive lelernent having one portion anchored at its end and the other portion being freely movf able with a contact at the end thereof and including a stationary contact normally engaging the movable contact, an electric heater in juxtaposition to the anchored portion of said heat-responsive element for transmitting heat thereto to cause deflection of said heat-responsive element with separation of the movable contact from said stationary Contact; and means for connecting said glow switch, said heat-responsive element and said heater in series in said circuit.

2. A starting relay for completing a circuit to a discharge lamp of the fluorescent type comprislng a casing, a glow switch disposed in said casing and having normally separated contacts` adapted to close the circuit to said lamp upon the occurrence of a glow discharge in said glow switch, and a thermal switch including a stationary contact and a heat-responsive element having one portion anchored at its end and the other portion being provided with a movable contact normally tensioned into engagement with said stationary contact, an electric heater in juxtaposition tothe anchored portion of said heat-responsive element for transmitting heat thereto to cause deflection of s'aid heat-responsive" element with separation of said movable contact from said stationary contact, and the contact-carrying portion of said heat-responsive element being operable when heated by the heat generated upon closure of said contacts under load to increase the contact pressure thereof with said stationary contact and eliminate chattering; and means for connecting said glow switch,

said heat-responsive element and said heater in series in said circuit. I v

3. A starting relay for completing a circuit to a discharge Alamp of the fluorescent type comprising a casing, a glow switch disposed in said casing and having normally separated contacts adapted to close the circuit to said lamp upon the occurrence of a glow discharge in said glow switch, and a thermal switch including a stationary contact and a U-shaped bimetallic element having an end of one of its legs anchored and the end of its other leg being provided with a movable contact normally tensioned in engagement with the stationary contact, an electric heater in juxtaposition to the anchored leg of the bimetallic element for transmitting heat thereto to cause deilection of said bimetallic element with separation of said movable contact from said stationary contact, and the free oontact-carrying leg of said bimetallic element being operable when heated by the heat generated upon closure of said contacts under load to increase the contact pressure thereof with said stationary contact thus eliminating chattering; and means for connecting said glow switch, said bimetallic element and said heater in series in said circuit.

4. A thermal relay for starting discharge lamps of the fluorescent type comprising a base, a stationary contact carried by said base, a heat-responsive element having a portion anchored at one end to said base and another portion freely movable and having a contact afilxed to the end thereof normally tensioned in engagement with said stationary contact, and an electric resistance heater in juxtaposition to the anchored portion of said heat-responsive element forA transmitting heat thereto to cause deflection of the anchored portion in one direction and movement of the other portion in an'opposite direction with attendant separation of said contacts.` y

' 5. A thermal relay for starting discharge lamps of the iiuorescent type comprising a base, a stationary contact carried by said base', a heat-responsive element having a portion anchored at one end to said base and another portion freely' movable and having a contact amxed to the end. thereof normally tensioned iny engagement with said stationary contact, an electric resistance heater in juxtaposition to the anchored portion of said heat-responsive element for transmitting heat thereto to cause deilection o! the anchored portion in one direction and movement of the other portion in an opposite direction with attendant separation of said contacts, and the contact-carrying portion of said heat-responsive element being movable in the same direction as said anchored portion when heated by the heat generated upon closure of said contacts under load to increase the contact ypressure thereof with said stationary contact thus eliminating chattering.

6. A thermal relay for starting discharge lamps of the fluorescent type comprising a casing provided with contact terminals adapted to engage a socket, a base within said casing provided with a stationary contact carried thereby, a bimetallic element having a portion anchored at one end to said base and another portion freely movable and having a contact aihxed to the lend thereof normally tensioned in engagement with said stationary contact, an electric resistance heater in juxtaposition to the anchored portion ot said bimetallic element for transmitting heat thereto to cause deilection of the anchored portion in one direction and movement of the other portion in an opposite direction with attendant separation of said contacts, and the contact-carrying portion oisaid bimetallic element being movable in the same direction as said anchored portion when heated by the heat generated upon closure of said contacts under load to increase the contact pressure thereof with said stationary contact thus eliminating chattering.

7. A thermal relay for starting discharge lamps of the fluorescent type comprising a casing provided With contact terminals adapted to engage a socket,'a base within said casing provided with a stationary contact carried thereby, a U-shaped bimetallic element having one leg thereof -anchored at its .end to said base and the other leg freely movable and having a contact aiilxed to the end thereof normally tensioned in engagement with said stationary contact, an electric heater in juxtaposition to the anchored leg of said bimetallic element for transmitting heat thereto to cause deilection of the anchored leg in the direction of the heater until it contacts the latter to restrain further deflection and to cause movement ot the other leg in an opposite direction with attendant separation ot said contacts, and the contact-carrying leg of said bimetallic element being movable in the same direction as the anchored leg undner innuence of heat generated by arclng of said contacts under load to increase tensional engagement of said contacts and eliminate chattering thereof. CHARLES H. HODGKINS.

ROBERT F. HAYS, Jn. 

